docs: def com_google_fonts_check_metadata_unique_full_name_values(family_metadata):
    """METADATA.pb: check if fonts field only has
       unique "full_name" values.
    """
    fonts = {}
    for f in family_metadata.fonts:
      fonts[f.full_name] = f
  
    if len(set(fonts.keys())) != len(family_metadata.fonts):
      yield FAIL, ("Found duplicated \"full_name\" values"
                   " in METADATA.pb fonts field.")
    else:
      yield PASS, ("METADATA.pb \"fonts\" field only has"
                   " unique \"full_name\" values.")